1. Field of the Invention
The invention relates to manufacture of neutron detectors, and specifically relates to coating boron lined neutron detectors.
2. Discussion of Prior Art
Recently, high sensitivity neutron detectors for homeland security have become increasingly important and increasingly in demand. Many known neutron detectors utilize He-3, a neutron sensitive material known to provide a detector of high sensitivity. The He-3 is provided within a volume that includes a cathode within a detection arrangement. Recently, the availability of He-3 has been has become insufficient to satisfy the demand associated with high sensitivity neutron detectors. Other than He-3 there are only a few neutron sensitive materials that are useful for constructing a neutron detector, including certain isotopes of uranium, lithium and boron.
Focusing upon boron, the majority (e.g., approximately 80%) of naturally occurring boron is B-11, which has 5 protons and 6 neutrons, and the remainder (e.g., approximately 20%) is boron 10 (B-10), which has 5 protons and 5 neutrons. The B-10 isotope is useful for neutron detection. Thus, for use in a neutron detector, it is typically desirable to enrich the concentration of B-10.
The detection of neutrons is based on the generation of secondary radiations at a converter material. With B-10 (10B) as the converter material, the reaction is described as follows when a neutron is captured:
10B+n→7Li+4α(2.792 MeV, ground state) and 7Li+4α+0.48 MeV γ (2.310 MeV, excited state)
The energy released by the reaction is approximately 2.310 million electron volts (MeV) in 94% of all reactions (2.792 MeV in the remaining 6%), and equals the energy imparted to the two reaction products (the energy of the captured neutron is negligible by comparison). The reaction products, namely an alpha particle (a) and a lithium nucleus (7Li) are emitted isotropically from the point of neutron capture by B-10 in exactly opposite directions and, in the case of the dominant excited state, with kinetic energies of 1.47 MeV and 0.84 MeV, respectively. As such, the use of boron as a neutron sensitive material is known and useful. Herein after boron may be discussed generically with the understanding that the content of B-10 is suitably sufficient.
Focusing for the moment upon the physical construction of neutron detectors, a detector includes an anode and a cathode. One example detector includes a wire extending on an axis for the anode and a cylindrical cathode circumscribing the anode. The cathode is lined with neutron sensitive material such as boron.
Known techniques for providing a boron lining within a neutron detector include the use of borane gas, which is decomposed to provide the boron lining as a precipitate, and the use of mineral oil, which carries boron in a suspension. However, with the increased demand for boron-based neutron detectors, such known techniques may not adequately/effectively/economically satisfy the demand.
A new generation of neutron detector production would be most beneficial.